Senior Liberal Democrats had been secretly preparing for a possible coalition for some years. The leader knew that coalition might be necessary. At the same time, I was worried by the likely electoral consequences of coalition for the party. In a confidential memo to the leader I warned that "the loss of our independence and acceptance of collective government responsibility would hit us hard in the polls". I was also asked to study the effects of coalition on our European sister parties where coalitions are the norm. I reported that few of them handled it well and that the junior party generally lost support. I said that in the event of coalition we would go down to 10%.

The leader was Paddy Ashdown, and the year was 1998.

The context was that before the previous year's general election, Ashdown had been led to believe that Tony Blair would endorse proportional representation. Labour had promised an early referendum on the best proportional alternative to first past the post. Twelve years later, the electoral arithmetic meant that the Lib Dems had to settle for much less and from a different party. The legacy of Tony Blair's "Journey" turned out to be three years of Gordon Brown's premiership and David Cameron's entry into Downing Street. Labour is happy to blame the Lib Dems for everything that happens now and is equally happy to absolve itself of any blame for losing around 150 seats to the Conservatives during this period.

This leaves the Liberal Democrats shaken by the drop in poll support but not entirely surprised by it. My view is that the drop in support should not be regarded as inevitable on polling day in 2015. In December 1996, the Lib Dems were suffering from too close an association with Labour and a poll rating below 10%. Analysis of the new parliamentary boundaries showed that the Lib Dems were down to 18 seats. Ashdown's profile differentiating ourselves from Labour (and the Conservatives) raised our share of support to 17% by polling day. More significantly, our campaigns in the new constituencies bucked the national swings and resulted in us more than doubling our number of MPs to 46.

We were still in great difficulty at the start of the 1997 general election (11% in the polls). But during that campaign we were able to establish clear differences with both other parties and we were able to do so with regard to issues that were the major concerns of the voters – as opposed to the sort of concerns that may motivate our members more. We made plain our differences with both other parties on issues like crime, health and education, and said rather less about constitutional reform.

I always told candidates to think as much about the psychology of Maslow's "hierarchy of needs" as any market research. This explains why issues such as the economy and the future of the NHS matter so, so much when people consider voting choices. These issues are bound to be at the forefront of the next election campaign. Some aspects of the coalition agreement will inevitably come back to haunt the Lib Dems. But the party will be helped by people's fears of Ed Miliband and Ed Balls being jointly responsible for economic management and ongoing fears about what would happen if the Conservatives had complete freedom of manoeuvre on issues such as the NHS.

Lib Dems must this week reassure people that any changes in the NHS are in the interests of patients – and explain that this would not necessarily have been the case without their influence. The workings of a coalition make it harder to express differences of opinion than during a general election campaign. But the lesson that I learned from our European sister parties was that "successful coalition requires a good measure of agree to disagree as well as compromise".